Photophysical characteristics of 4,4′-bis( N-carbazolyl)tolan derivatives and their application in organic light emitting diodes

Abstract

4,4′-bis( N-carbazolyl)tolan ( BCT) and 4,4′-bis[ N-(3,6-di- t-butyl)carbazolyl]tolan ( BCT- t -Bu) were synthesized as π-expanded analogs of 4,4′-bis( N-carbazolyl)biphenyl. Their photophysical characteristics both in solution and films were thoroughly investigated. Interestingly, the phosphorescence spectrum of BCT was significantly medium-dependent, and the emission maximum was red-shifted by 131 nm from 489 nm in solution at 77 K to 620 nm in a deposited film at 5 K, suggesting the presence of strong intermolecular interactions in the film. BCT and BCT- t -Bu were found to be useful as host materials for fluorescence-based organic light emitting diodes (OLEDs). However, their low triplet energy levels in films negated their potential to act as hosts in phosphorescence-based OLEDs.